The formation of gas hydrates has long been recognized as a potential problem in the oil and gas industry. During recent years the general trend within the industry to make more efficient designs and to minimize cost wherever possible has led to considerable effort to understand hydrate formation and methods to prevent or inhibit such formation.
Gas hydrates are solids that form from a combination of water and one or more hydrocarbon or non-hydrocarbon gases. In physical appearance, gas hydrates resemble packed snow or ice. In a gas hydrate, the gas molecules are “caged” within a crystal structure composed of water molecules. Sometimes gas hydrates are called “gas clathrates”. Clathrates are substances in which molecules of one compound are completely “caged” within the crystal structure of another. Thus, gas hydrates are one type of clathrate.
Two broad techniques are generally used to overcome or control hydrate formation, namely thermodynamic and kinetic, which can be used alone or in conjunction. For the thermodynamic approach, there are a number of reported or attempted methods, including water removal, increasing temperature, decreasing pressure, addition of “antifreeze” to the fluid and/or a combination of these. For the kinetic approach, attempts have been made to (a) prevent the smaller hydrocarbon hydrate crystals from agglomerating into larger ones (known in the industry as an anti-agglomerate) and/or (b) inhibit, retard and/or prevent initial hydrocarbon hydrate crystal nucleation; and/or crystal growth (known in the industry as a kinetic hydrate inhibitor).
Kinetic efforts to control hydrates have included the use of different materials as inhibitors. For instance, onium compounds having at least four carbon substituents have been used to inhibit the plugging of conduits by gas hydrate. Also, additives such as polymers with lactam rings have been employed to control hydrates in fluid systems, for example:
U.S. Pat. No. 6,867,262 discloses a graft polymer gas hydrate inhibitor wherein the graft polymer comprises a base polymer and vinyl caprolactam (in ethylene glycol) grafted onto the base polymer;
U.S. Pat. No. 6,451,892 discloses a composition that includes a homopolymer of vinyl caprolactam, a glycol ether polymerization solvent, a carrier solvent and optionally water or methanol;
U.S. Pat. No. 6,359,047 discloses a composition comprising a copolymer based on vinyl caprolactam and N,N-diethylaminoethyl meth(acrylate) in admixture with a low molecular weight glycol ether as a hydrate inhibitor;
U.S. Pat. No. 6,281,274 discloses the use of a hydrate inhibitor composition comprising a copolymer of vinyl caprolactam and vinyl pyridine made in 2-butoxyethanol;
U.S. Pat. No. 6,242,518 teaches a gas hydrate inhibitor composition comprising a homopolymer of vinyl caprolactam made in a mixture of a glycol ether and water;
U.S. Pat. No. 6,194,622 teaches a method for inhibiting hydrate formation using a copolymer of a surfactant monomer and vinyl caprolactam in admixture with an alcohol or glycol;
U.S. Pat. No. 6,180,699 discloses the use of a homopolymer of vinyl caprolactam, made in a glycol ether, and a polyoxyalkyldiamine or polyoxyaryldiamine as a hydrate inhibiting composition;
U.S. Pat. No. 6,096,815 discloses a composition for preventing the formation of gas hydrates comprising a homopolymer of vinyl caprolactam and an alcohol containing 3 to 5 carbon atoms;
U.S. Pat. No. 5,880,319 teaches a method for using an N-vinyl lactam polymer and an alcohol to reduce the tendency of clathrate agglomeration;
U.S. Pat. No. 5,874,660 discloses a method for inhibiting hydrate formation using a kinetic hydrate inhibitor comprising a polymer formed from N-methyl-N-vinylacetamide and vinyl caprolactam in water, brine or low molecular weight alcohols; and
U.S. Pat. No. 5,432,292 discloses a method for controlling clathrate hydrates in fluid systems utilizing a terpolymer comprising N-vinyl caprolactam.
Notwithstanding the state of the technology, it is an object of the present disclosure to provide a method for producing an improved poly(vinyl caprolactam) polymer and the use of such polymer as a kinetic hydrate inhibitor in the transport of natural gas and/or liquid hydrocarbons through a conduit or as a component in a personal care composition.